Stabilized tetragonal zirconia fibers and textiles

ABSTRACT

Zirconia fibers and textiles that are stabilized in the tetragonal form by small, carefully controlled amount of oxides of the metals of Group III B of the Periodic Table. The stabilized tetragonal zirconia fibers and textiles are useful as refractories, thermal insulators, battery spacers, fuel cell spacers, and the like.

States 11 tet 1191 Hamling 1 Jan. 14, 1975 [541 STABILIZED TETRAGONAL ZIRCONIA 3,222,148 12/1965 Hay 1. 106/57 x FIBERS AND TEXTILES 3,385,915 5/1968 Hamling .1 264/05 X 3,416,953 12/1968 Gutzeit et al. 106/57 X [75] Inventor: Bernard H. Hamlmg, Warwick, 3.634113 1/1972 Fehrenhachcr' 106/57 X N.Y. 3,663,182 5/1972 Humling 1. 264/05 X [73] Assigncc: Union Carbide Corporation, New

York Primary Examiner-Benjamin R. Padgett [22] Filed; May 1, 1972 Assistant Examiner-R1 E. Schafer Attorney, Agent, or Firm-William Raymond Moran [21] Appli No.2 249,057

Related US. Application Data [63] Continuation of Ser. No. 700.031. Jan. 24, 1968, [5 T ACT abandoned.

I Zirconia fibers and textiles that are stabilized in the [52] US. Cl. 252/301.1 R, 106/57, 264/05 tetragonal form by small, carefully controlled amount [51] Int. Cl C09k 3/00 f xid f h m tals of Group III B of the P ri dic [58] Field of Search 252/30l.l R; 106/57; Tab e. The stabilized tetragonal zirconia fibers and 264/05 textiles are useful as refractories, thermal insulators,

battery spacers, fuel cell spacers, and the like.

[56] References Cited v UNITED STATES PATENTS 4 Claims, N0 Drawings 3,180,741 4/1965 Wainer 106/57 X STABILIZED TETRAGONAL ZIRCONIA FIBERS AND TEXTILES This is a continuation, of application Ser. No. 700,031 filed Jan. 24, 1968 now abandoned.

bilized zirconia fiber ortextile will have the same form as the original fiber or textile, although the dimensions will be reduced.

The zirconium compound and Group III B metal The invention relates to zirconia fibers and textiles 5 Compound are normally introduced m the Organic that are stabilized in the tetragonal form by small, carefully controlled amounts of oxides of the metals of Group III B of the Periodic Table, and to a process for producing the stabilized tetragonal zirconia fibers and textiles. I

Zirconia (ZrO has a fusion point of 2677C., and is therefore a very useful refractory material. However, pure zirconia bodies are rarely used as refractories because of a phase change that occurs near l,O00C. Below l,O00C., pure zirconia exists in the monoclinic form, and when heated above 1000C., it tranforms to the tetragonal form. The phase change at about l,O00C. is accompanied by a large volume change which would cause a pure zirconia article to shatter. However, it is known that zirconia can be stabilized by firing with certain other refractory oxides to produce the cubic form which is stable over a wide range of temperatures. For instance, zirconia is frequently stabilized in the cubic form by firing to 1,700C., or higher with 11.5 to weight percent yttria, by firing to 1,550C. or higher with 8 to 15 percent magnesia, or by firing to 1,500C. or higher with 6 to 15 weight percent calcia. Zirconia can also be stabilized in the cubic form by silica, scandia, and oxides of the rare earth metals (i.e., lanthanide metal-oxides). Discussions of known methods for stabilizing zirconia can be found on pages- 364-367 of Oxide Ceramics by Eugene Ryshkewitch, Academic Press, New York (1960) and on pages 77-81 of HighTemperature Technology, edited by I. E. Campbell, John Wiley and Sons, Inc., New York.

The present invention is based upon the discovery that zirconia fibers and textiles can be stabilized in the tetragonal form by small, carefully controlled amounts of oxides of metals of Group III B of the Periodic Table.

The oxides of metals of Group III B of the Periodic Table which are useful as stabilizers in this invention include scandia, yttria, oxides of the rare earth metals such as lanthana, ceria, and the like, and oxides of the metals of the actinide series such as uranium oxide. The preferred metal oxide stabilizers are yttria, ceria, and mixed rare earth metals oxide stabilizers can be used in mixture, if desired.

The stabilized tetragonal zirconia fibers and textiles are produced by the relic process which is described and claimed in copending application Ser. No. 576,840, now US. Pat. No. 3,385,915 filed Sept. 2, 1966, Metal Oxide Fibers, Textiles and Shapes and Process for Producing Them, by Bernard H. Hamling, and in Belgian Pat. No. 697,315, filed Apr. 20,- 1967 and made available to the public in late October, 1967. Briefly, the relic process for producing stabilized tetragonal zirconia fibers and textiles comprises the steps of:

a. impregnating an organic polymeric fabric or textile with a mixture of a zirconium compound and a Group III B metal compound, and

b. heating the impregnated fabric or textile, at least partly. in an oxidizing atmosphere, in order to carbonize and volatilize the organic polymer without igniting said polymer, and at the same time to insure conversion of the-zirconium and Group III B metal compounds to their oxides. The resulting stapolymeric fabric or textile in solution. The solvent is preferably water, but suitable organic solvents can be used also. The action of the solvent apparently swells the amorphous matrix of the fiber polymer, thereby opening the interstices between the small crystallites of polymer chains (micelles or microfibrils). The dissolved metal compounds enter the swollen amorphous regions and become trapped there between the crystallites when the solvent is removed.

The precursor fiber or textile can be in the form of yarn, monofilaments, knitted textiles, woven textiles, and felts and other non-woven textiles, especially wherein the individual fibers have been interlocked to some extent by processes such as needle punching.

The precursor fibers or textiles can be made from any organic polymer provided that the polymer is characterized by the above-described structure of extremely small crystallites held together in a matrix of amorphous regions which enlarge and admit the metal compounds upon immersion in the metal compoundscontaining material, which is usually a solution of the said metal compounds. Cellulosic materials such as rayon, saponified cellulose acetate, cotton, linen, and the like can be used as the fiber or textile. The fiber or textile can also be wool silk, acrylics, polyesters, polyamides, and polyurethanes. Preferred fabrics and textiles are those made from rayon. I

Many different zirconium compounds and Group III B metal compounds can be used to impregnate the precursor fiber or textile. Specific illustrative examples include zirconyl chloride, zirconium acetate, zirconium,

Following impregnation of the fiber or'textile with the metal compounds from a solvent solution, it is preferred to remove excess solution from the surfaces of the individual fibers in order to prevent accumulation of caked metal compound. This can be done by blotting, pressure rolling, centrifugation, or the like. The impregnated fiber or textile is then dried, for example, by air drying or heating in a stream of warm gas, prior to the heating steps which volatilize the organic polymeric presursor fiber or textile and form the tetragonal zirconia.

The heating step for volatilizing the precursor fiber or textile and forming the metal oxide is carried out under controlled conditions so as to avoid ignition of said fiber or textile. As an example of such controlled conditions, an impregnated cellulosic fiber or textile is heated in air to a temperature between about 350C. and 900C. at a rate of not more than about C. per hour. Much faster heating timescan also be used, as long as ignition of the precursor fiber or textile is avoided. After the initial formation of the metal oxide (which can occur at temperatures as low as about 350400C.), a bake at 500600C. or higher is desirable in order to achieve maximum. elimination of impurities and densification of the zirconia.

The zirconia fibers and textiles are produced in the tetragonal form and they are stabilized in that form by about 20 percent of the monoclinic form can be present in many cases without detrimental effect). the zir conia known to the prior art could be prepared in a temperature and corrosion resistant applications. The stabilized zirconia fibers and textiles can be used as battery separators, fuel cell separators, pipe liners and troughs for transferring molten metal, heat shields, and

sired in order to achieve the bestphysical properties. The stabilized tetragonal zirconia fibers and textiles of the invention have enhanced utility in many high metastable tetragonal form by decomposing a zirco- 5 the likenium compound in air at temperatures below about The a P eS beiOW trate t e i e 600C. (usually between about 500 and 600C). However, such metastable zirconia reverted to the mono- EXAMPLE 1 clinic form when heated above about and A series of zirconia cloths containing varying proporthereafter its behavior with respect to crystallographic {ions of yttria were produced by the relic process The Phase Changes was identical to that Of Conventional initial cloth substrate was square weave, textile rayon. zirconia. The Group III B metal oxide stabilizers pre- Th rayon was proswollon in ]N hydrochloric acid, Vent this reversion to TiiOiiOCiitliC form at 600C then rinsed in water. The cloth was impregnated by im- The Group iii B metal Oxide Stabilizer is Used in a mersing it for 18 hours in 2.5 molar aqueous ZrOCl small, stabilizing amount sufficient to maintain at least containing varying quantities of YCl The impregnated about 80 percent of the zirconia fiber or textile in the cloth was centrifuged three times at 4,0004,600 rpm tetragonal form when said zirconia fiber or textile is in an ll-inch diameter basket for a total of 20 minutes heated at about 800C. for about one hour. The exact in order to remove excess salt solution. The cloth was amount of stabilizer to be employed varies somewhat then heated in a forced air oven. The initial temperawith the exact nature of the Group III B metal oxide 20 ture was C., and the temperature was gradually instabilizer. For instance, it has been found that from creased overaperi of 24 hours toafinal temperature about 0.5 to about 4, and preferably from 2 to 4, mole of 650C. Thereafter, the cloth was fired as indicated percent of yttria (-Y O based upon moles of zirconia in Table 1 below. 7 plus yttria, are effective stabilizing amounts. Amounts Table 1, below, displays the YCl content of the imof from about 5 to about 20 weight percent of ceria, 25 pregnating solution, the mole percent Y O in the ZrO based upon weight of zirconia plus ceria, have been cloth, and the crystallographic phases in the cloth after found to be effective stabilizing amounts. Amounts of heat treating in air. The crystallographic phases were from about 5 to about 20 weight percent of mixed rare determined at room temperature by X ray diffraction earth oxides, based upon weight of zirconia plus mixed analysis. In Table I, M, T and C denote the monoclinic, rare earth oxides, have been found to be effective stabitetragonal, and cubic phases, respectively, present in lizingamounts. the ZrO cloths.

TABLE 1 Crystallographic Phases of ZrO /Y O Cloth YCl Content Crystal Structure After: Cloth of Solution Mole YZOQ l hr. at 1 hr. at l hr. at 1 hr. at

No. Gm/liter in Cloth 1000c 1200C 1400C l400 C l. 0 0 93%M 100%M 100%M I00%M 2 3.6 1.29 90 7?; lOOVcM IOOYrM 1007rM 10%T 3 7.2 2.08 )%M 43%M sh /(M loo /FM 91%T 57%T i /(T 4 13.9 2.73 wo /(T lO07rT loo /hr l00 /rT 5 26.2 5.52 l00"/rC l00'7rC 100%C lOOVrC 6 37.4 7.10 100%(3 100%C iooac ION/(C 7 47.8 9.57 100%(2 lOO /rC 100m loo /(c The exact amount of stabilizer oxide that is desired EXAMPLE 2 to used. p to extent upon end use of A free-standing zirconia thermal insulation heat the zlrcmna fiber l In gw the excel shield was fabricated. The heat shield assembly conlent refslstance of zlrcoma to alkali lmpoitami sisted of two half-cylinders measuring 4.3 inches interwherem the tempfrature not excesswely high nal diameter by 7.0 inches tall,with top and bottom cirfrom 300 r to 500 as t as mole Percent cular plates. The wall thickness of the cylinder varied yttria can be employed. An addition level of about 2 to from (H50 to 0200 inch The ham shield was 4 mole percent yttria is desired to enable the zirconia duoed by the f ll i procedure; fiber o i i be fi F t 8000400900 range Thirty mil satin weave zirconia cloth containing 2.2 eliminate impurities a P i maximum 60 mole percent yttria stabilizer was produced from rayon densification, and to thereby achieve maximum chemiby tho roho process by a procedure analogous to that cal resistance- As u as 10 Or 20 Percent of mOnO- described in Example l.'The cloth was fired to a final clinic zirconia is permissible in such uses. When the zirtemperature f ]()0()C Th i i l h was then Conia is to be Used at tempfiraiures above i -i impregnated with azirconiacement and wound around from about 2 to 4 mole P yttria is normally a cylinder to give a six-layer laminate. The zirconia cement is a mixture of parts by weight of an aqueous solution of basic zirconyl chloride i.'e., ZrO(OH)Cl'n- H 0, and yttrium trichloride (Sp, Gr. of the solution was 1.65 at about room temperature) in proportions to an aqueous solution of zirconyl chloride and yttrium trichloride, followed by'dry ball milling of the decomposition product for 20 hours and passing the powder through a 400 mesh screen. The weights of the cloth and cement was 340 and 220 grams, respectively. The laminate was then tired to a temperature of 1,000C., over a period of 4 hours.

The heat shield was placed inside a tungsten-heated vacuum furnace. The furnace was cycled through twenty rapid heating and cooling cycles ranging from room temperature to 850C. to 2,000C. with no appar ent damage to the heat shield other than a slight amount of warping. Unstabilized zirconia would have shattered during this test, probably during the first cycle.

EXAMPLE 3 Ten-mil zirconia satin weave cloth containing 4.56 weight percent yttria (i.e., 2.5 mole percent yttria) that was prepared by the relic process from rayon cloth, was fired to various temperatures and then immersed in 75 weight percent aqueous potassium hydroxide for 50 hours at 410F. Table II, below, displays the firing times and temperatures (in air) and the tensile strengths be fore and after immersion in potassium hydroxide.

TABLE II filaments. The rayon cloths were soaked for 17 hours in an aqueous solution of zirconyl chloride having a specific gravity of 1.400 i .002 and which contained varying amounts of yttrium trichloride. The impregnated cloths were wet rolled once through rolls having an 8 ton nip load at a speed of 3.0 rpm. After air drying the cloths were again rolled once: at the same conditions. The heating schedule was analogous to that described in Example 1, to a final temperature of 6009C.

Table [11, below, displays the amounts of yttria and zirconia (as YCI and ZrOCl in the impregnating so lutions and the weights of the rayon cloths that were used as the precursor fabric:

The maximum retention of strength was found with the cloth that was fired to 1,000C. Unstabilized zirconia cannot be heated to temperatures nearly as high as 1,000C. without forming the monoclinic phase which is not nearly as chemically resistant as the tetragonal phase, probably because the individual crystals are much larger in the monoclinc phase. All five ZrO cloths stabilized with Y O were still intact after contact with KOH and could be recovered from the KOH solution.

EXAMPLE 4 A series of zirconia cloths were made by the relic process analogous to the procedure described in Example 1. The precursor cloth was S-harness satin-weave cloth using textile rayon yarn of 1,100 denier and 480 Sample Maximum Hrs. at Tensile StIengthJb/inch No. Temp. C Temp. Before Immersion After .lmmersion 1 650 5 0.8 0.02 2 700 l 1.0 0.02 3 800 l 0.7 0.05 4 900 l 0.9 0.17 5 1000 1.0 0.47

TABLE III Grams Y O (as Grams ZrO "'(as Ycl per liter of ZrOCl per liter of Cloth Mole Per lmpregnating lmpregnating Weight of No. Cent Y O Solution Solution Rayon Cloth Zirconyl chloride and yttrium trichloride are often supplied commercially labeled with an assay of the number of grams per equivalent of the oxide.

7 8 Table 1V,below, displays the mole percents of yttria S l C I (C 0 Z 0 9 1 2 0 1.11.1011 erlum XI 0 C r 2 [3V] y found 1n the cloths (which, it W1 be noted, are not gmflilcr 2 gm'lmer v of Solution Montreal to the amounts that were in the impregnating 1 17.5 291 1.40 solut1ons), and the crystallograph1c phases after heat 2 252 280 L40 treating for the indicated times. 5 3 39.5 264 1.40

TABLE IV Crystallographic Phases Present in 7,r() /Y,() (lnths After Heat Treatment in Air (M m01i0elinic;'l' tetr;1go11t1l;('-- cubic) Y Y 2 hours 1 hour 1 hour I hour 1 hour Cloth Content Content 111 at :11 at 211 No. mole wt. '7: 600C X00"(' l000"( |200C 1400( l 0 0 NWT 6071-1 1 471 1- 9%M 40% M 8678M 100%M 100%M 2 0.55 1.0 91%T 80%T 24%T 9%M %M 96%M 100%M 100%M 3 0.72 1.3 '93%T 89%T %T 9%M 77PM 1121M 7572M 91%M 100%M 4 0.93 1.7 937rT 89'/rT 51%T 12%T 7%M ll7rM 49%M 8871M 100%M 5 1.0 1.8 92"/T 90/(T %T 18%T 4%T 8"/rM 1071M 5571M 8271M 96%M 6 1.3 2.3 947lT 947rT 87%T 25%T 13%T 6/rM fr /1M 1376M 7521M 87'VrM 7 1.4 2.6 93"/1T 93%T 937(T 24%T 872T v 772M 7%M 776M TM 72%M 8 1.8 3.3 94%T 93%T 92%T 49%1 46%T 6%M 7%M 8%M 51%M 54%M 9 2.4 4.3 95711 9'3'/(T 94%T 97%T 100%T 521M 7%M 671M 3%M 10 3.4 6.2 10071'1' l00l (T 97%T 100%T 100%T 3%M 11 3.8 6.9 957rT 96 7IT 100%T l007rT 10071T 5'71M 4 /(M l2 7.6 13.9 100 /1C, 10071C 100%C 1007rC .1007rC I Table V, below, displays the tensile strengths of the Zirconia cloths after heat treatment in air at the indi- I cated temperatures. solutions for a period of 19 hours at 70F.

TABLE V Tensile Strengths olZrO-JYIO Cloths After Heat Treatment in Air The rayon fibers were impregnated with thesalt by immersing 266 gm. of rayon in each casein the above YZO3 YIOJ 1 hour 1 hour 1 hour 1 hour Cloth Content Content at at at at NO, 111016 /r wt. "/1. 800(." 1000C 1200c' 1400c l 0 0 0.44 0.46 too weak for measurement 2 0.55 1.0 1.20 0.97 too weak for measurement 3 0.72 v 1.3 1.92 0.58 too weak for measurement 4 0.93 1.7 1.28 0.53 0.46 .5 1.0 1.8 1.45' 0.90 0.82 6 1.3 2.3 1.91 1.48 0.77 7 1.4 2.6 2.39 2.54 0.57 0.40 8 1.8 3.3 2.38 2.98 1.48 1.04 9 2.4 4.3 2.96 2.83 5.61 2.84 10 3.4 6.2 4.22 4.32 5.23 8.19 11 3.8 6.9 3.51 4.95 6.89 5.61 12 7.6 13.9 0.93 2.56 1.84 2.63

Reported in lh/in. Average of two pulls on each sample.

EXAMPLE 5 The fibers were subsequently treated in a manner analogous to Example 4 to convert the salt-loaded Tetragonal Stabilization of Zirconia Fibers with Cerayon fibers to oxide fibers. The three fibers were dei id I termined by x-ray diffraction analysis to be composed stabilized Zirconia fibers containing additions f 60 oftetragonal zirconia. The fibers conta1ned,6.99, 10.70

and 16.95 weight percent cerium oxide, based upon total weight of fibers. The fibers containing the smallest amount of cerium oxide also contained 13 percent monoclinic zirconia. All three fibers were heated to 1000C.

EXAMPLE 6 Tetragonal Stabilization of Zirconia Fibers with Rare Earth Oxide to chemical attack by concentrated aqueous potassium hydroxide. (Potassium hydroxide is employed as the electrolyte in many secondary (rechargable-type) batteries and fuel cells and chemical and physical stability Wilt; uficd lhll Chloridc' $811 which is commercially 5 of electrode separators used in contact with the elecava1lable and had the following composition: t l t often at temperatures in the range of Rm Eanh Oxide Pcmmage by wcigh 200-500?F. 1s lmportant to the efficlent operatlon of these devlces. 1.21 24 CeO 48 Pr,o,, The SIX cloths wereimmersed in 75-85 percent pogidzol tassium hydroxide (-25 percent H O) held at 400F'.

1,0, 3 (M203 2 for a period of 360 hours. After this perlod they were YQOH 0.2 removed from the solution and washed free of potassium hydroxide with water. All cloth specimens were Three aqueous solutions (2000 ml. each) used for 15 recovered from the solution intact and had undergone impregnation of the rayon fibers contained chloride no damage or changes visible to the eye. Weight salts having equivalent oxide compositions listed changes and strengths of the cloth specimens after 360 below: hours contact with KOH at 400F. are listed below:

TABLE VI Breaking Cloth Weight Loss Strength No. Oxide Stabilizer Per Cent lb./inch width 1, Example 6 6% Rare Earth Oxide 12.8 1.7 2, Example 6 9% Rare Earth Oxide 10.4 2.8 3, Example 6 15% Rare Earth Oxide 6. 6 3.3 1, Example 5 6% Cerium Oxide 27.4 0.1 2, Example 5 9% Cerium Oxide 5.4 1.8 3, Example 5 15% Cerium Oxide 2.5 2.8

Solution Rare Earth Oxide Zr0 Specific Gravity What is l i ed is;

No. gm./liter gm./liter of Solution 1. Fibrous z1rcon1a containing an mode of a metal of 1 17.3 289 1.40 Group III B of the Periodic Table, said oxide being se- 5 23's g2: :38 lected from the group consisting of scandia, lanthana, ceria and mixed rare earth oxides, said oxide being present in an amount of from about 5 to about 20 per- The rayon fibers were impregnated with the salt mixcent based upon weight of zirconia plus oxide to mainture by immersing 266 gm. of rayon in each case in the tain at least about 80 percent of said fibrous zirconia in above solutions for a period of 19 hours at 70F. the tetragonal form when heated at about 800C for The fibers were subsequently treated in a manner 40 about one hour. analogous to Example 4 to convert the salt loaded 2. The fibrous zirconia of claim 11 wherein said Group rayon fibers to oxide fibers. The three fibers, heated to III B metal oxide is (a) from about 5 to about 20 weight 1,000C., were determined by x-ray diffraction analysis percent of ceria, based upon weight of zirconia plus to be composed of only tetragonal zirconia. The zircoceria, or (b) from about 5 to about 20 weight percent nia fibers contained 8.30, 10.30 and 16.55 weight perof mixed rare earth oxides, based upon weight of zircocent rare earth oxides, based upon total weight of finia plus mixed rare earth oxides. bers. 3. The fibrous zirconia of claim 1 wherein said fibrous zirconia is in the form of yarn, monofilament, EXAMPLE 7 knitted fabric, woven fabric, or non-woven fabric. 0 5O 4. The fibrous zirconia of claim 2 wherein said ii- The Oxlde fibers mffloth form Contammg the three brous zirconia is in the form of yarn, monofilament, levels of rare earth oxides (Example 6) and three levels knitted fabric Woven fabric, or nnmwoven fabric of cerium oxide (Example'S) were tested for resistance =1 

2. The fibrous zirconia of claim 1 wherein said Group III B metal oxide is (a) from about 5 to about 20 weight percent of ceria, based upon weight of zirconia plus ceria, or (b) from about 5 to about 20 weight percent of mixed rare earth oxides, based upon weight of zirconia plus mixed rare earth oxides.
 3. The fibrous zirconia of claim 1 wherein said fibrous zirconia is in the form of yarn, monofilament, knitted fabric, woven fabric, or non-woven fabric.
 4. The fibrous zirconia of claim 2 wherein said fibrous zirconia is in the form of yarn, monofilament, knitted fabric, woven fabric, or non-woven fabric. 